Power shift automatic gearbox for motor vehicles

ABSTRACT

An automatic powershift gearbox with at least one gearbox assembly for selecting the respective gear ratios and with at least one multiple-disk clutch capable of being actuated in a controlled manner for holding or releasing individual elements of the planet gear, which allows gear shift operations without interrupting the torque flow. The multiple-disk clutch comprises a first and a second disk set which are in mutual engagement and can be brought into friction engagement by axial compression against one another. The first disk set is connected with a first shaft, and the second disk set is connected with a second shaft. The multiple-disk clutch is coupled by a transmission with an electric machine comprising a rotor and a stator, for bringing the two disk sets into and out of friction engagement by means of the electric machine. The rotor of the electric machine is supported rotatably and axially movable on one of the shafts by means of a gearbox for converting a rotary motion into a thrust motion.

BACKGROUND OF THE INVENTION

The invention relates to an automatic powershift gearbox with at leastone gearbox assembly for selecting the respective gear ratios and withat least one multiple-disk clutch capable of being actuated in acontrolled manner for holding or releasing individual elements of theplanet gear, which allows gear shift operations without interrupting thetorque flow. The multiple-disk clutch comprises a first and a seconddisk set which are in mutual engagement and can be brought into frictionengagement by axial compression against one another. The first disk setis connected with a first shaft, and the second disk set is connectedwith a second shaft. The multiple-disk clutch is coupled by atransmission with an electric machine comprising a rotor and a stator,for bringing the two disk sets into and out of friction engagement bymeans of the electric machine.

DEFINITIONS

Automatic gearboxes for motor vehicles are distinguished by so-calledautomated gearboxes and so-called automatic powershift gearboxes, whichwith respect to their effect on the driving dynamics are based ondifferent concepts which are explained in more detail in the following.

STATE OF THE ART

In the state of the art it is know to realise automated gearboxes inthat in manually-operated gearboxes all gear shift operations which areusually carried out by the driver are taken over by an electronicallycontrolled actor system. With respect to driving physics this means thatduring a gear shift operation, a clutch must always be opened so thatthe torque flow is interrupted.

With the automatic powershift gearboxes which are also known in thestate of the art, it is also possible to shift gears under load. Withrespect to driving physics this means that also during a gear shiftoperation, the torque flow and thus the tractive power is notinterrupted.

A decisive difference between these two concepts is the marked reductionin comfort, in particular in passenger cars with high accelerationcapability or in vehicles with off-road use, where an interruption ofthe tractive power during the gear shift operation is not acceptable interms of driving physics.

Automatic powershift gearboxes carry out starting, selection of therespective gear ratios, and gear shifting automatically. As a startingelement, a hydrodynamic torque converter with or without lockup clutchfor eliminating the torque converter slip is usually employed which alsoserves for vibration damping.

For selecting the respective gear ratios several sets of planet gearsare used which are connected downstream of the hydrodynamic torqueconverter and whose number and arrangement depend on the number of gearsteps and the required gear ratios.

The individual elements of the planet gears are held or released bymeans of hydraulically operated multiple-disk clutches and multiple-diskbrakes, which permits gear shift operations without an interruption ofthe torque flow.

A gearbox control unit is used to define the respective gear steps andshift times as a function of the position of the selector lever, theaccelerator pedal position, the engine condition, and the velocity ofthe vehicle. The gearbox control unit is usually operatedelectronically/hydraulically.

A motor driven hydraulic pump provides for the supply of thehydrodynamic torque converter, the shift elements, and the gearboxcontrol unit with hydraulic pressure.

From WO 99/64756 a clutch assembly is known by means of which the speeddifferences of two shafts can be compensated. A clutch pressure plate isdisplaced in the axial direction by means of an electrically drivenmotor. For this purpose, the motor is arranged so that it surrounds oneof the shafts and is adapted to cause a hollow nut to rotate. The hollownut is supported at the housing of the electric motor and serves to movea hollow spindle in the axial direction, which is supported on theshaft. A further bearing is installed on the hollow nut, which carries adriver. This driver operates a spring which acts on the clutch pressureplate.

This is disadvantageous because of the high expenditures for thebearings of the electric motor and the hollow nut/spindle arrangement onthe shaft and in the clutch housing.

From DE 198 37 115 A1 a drive assembly for a motor vehicle is known inwhich an electric motor can be coupled by means of a locking device tothe drive train of the motor vehicle consisting of combustion engine,clutch, and output shaft. The concepts described in this documents are,however, very weak as far as their technical realisation is concerned.In particular, there is no indication for the realisation of the lockingdevice and its coupling to the drive train.

From DE 38 989 A1 an actuator for a friction clutch of amanually-operated gearbox is known, which couples two shaft sectionstogether. At the outside of a manually-operated gearbox an electricmotor is attached which actuates a piston valve via a threadedspindle/nut arrangement, which radially protrudes towards the shaft andis supported in an axial/radial ball bearing on the shaft. A leverengages the axial/radial ball bearing, which acts upon a clutch pressureplate which engages or disengages, respectively, the clutch.

In this case, too, the high expenditures for the bearings and theconsiderable space requirement of the overall arrangement aredisadvantageous.

Problem on Which the Invention is Based

The above described automatic powershift gearboxes have rotatinghydraulic actuators for the actuation of the hydraulically actuatedmultiple-disk clutches. Their seals are also subjected to rotation. Thisleads to considerable friction losses (up to 5% of the total torquetransmitted by the automatic powershift gearbox). In addition, theconcurrently occurring leakage of the hydraulic fluid results in anadditionally required pressure to be provided by the motor drivenhydraulic pump. Finally, the hydraulic operation of the multiple-diskclutches necessitates very high expenditures. Further, the abovedescribed arrangements with electric motors for the operation of themultiple-disk clutches are equipped with very expensive bearingarrangements.

The invention is therefore based on the object to modify these automaticpowershift gearboxes in such a manner that they are significantly moreeconomic and have a higher efficiency.

Inventive Solution

The inventive solution of this object consists in that in an automaticpowershift gearbox of the initially described type the rotor of theelectric machine is supported rotatably and axially movable on one ofthe shafts by means of a gearbox for converting a rotary motion into athrust motion. In other words, according to the invention the rotor ofthe electric motor is positioned within the overall arrangement, on theone hand, via its air gap to the stator and, on the other hand, via thegearbox for the conversion of the rotary motion into the thrust motion.

This completely novel configuration is advantageous in that theexpensive hydraulic cylinder/piston arrangement for the operation of themultiple-disk clutch, whose seals cause significant friction losses isomitted and replaced by an electric motor. The electric motor, may,however, produce losses (electric losses and others) during itsoperation, but in its end position in which the multiple-disk clutch isengaged or disengaged the losses should by minimised. The permanentfriction losses of the seals, however, are eliminated by the invention.The reason for this is, among others, that the rotor of the currentlesselectric motor can rotate with the same speed as the shaft carrying itso that no losses are occurring. This configuration further permits tohave the rotor act on the disk set which is also attached to this rotorso that not speed differences (and thus friction losses) occur betweenthe rotor and the disk set. This configuration provides a numberadditional advantages and benefits which will be explained in moredetail further below.

Advantageous Developments of the Invention

In a preferred embodiment of the invention the gearbox for converting arotary motion into a thrust motion consists of a spindle/nut arrangementone part of which is connected with one of the shafts in a non-rotatableand axially non-movable manner, and the other part of which is connectedwith the rotor in a non-rotatable and axially non-movable manner. Thisis a possibility to support the rotor on the shaft without necessitatingthe separate roller or ball bearings which are required in the state ofthe art.

According to the invention the rotor of the electric machine uponcurrent supply further carries out an axial movement relative to thesecond or the first, respectively, shaft, which depends on its speedand/or sense of rotation, and in the currentless condition hasessentially the speed of the shaft on which it is carried. This aspectof the invention represents a remarkable difference compared to theconfigurations according to the state of the art: According to theinvention the rotor is always co-rotating with the shaft carrying itwhen the electric motor is in the currentless condition. By variationsin speed and/or sense of rotation (caused by a respective currentsupply) of the rotor relative to the speed of the shaft, the rotorcarries out an axial movement (relative to the shaft) and operates themultiple-disk clutch. In the state of the art the electric motors arearranged as independent assemblies on/in the gearbox and operateindependently from the rotation of the shaft.

The rotor of the electric machine is further rotatably connected withthe disk set which is arranged at the shaft carrying the rotor, so thatupon an axial movement of the rotor the two disk sets come into and outof friction engagement. This rotatable connection can be realised insuch a manner that with the multiple-disk clutch being not in a frictionengagement the electric machine has virtually no connection with themultiple-disk clutch. Since, incidentally, the two disk sets areseparated from one another, no torque is transferred. The motor may, butneed not, be disconnected from the respective disk set. Regardless ofthis, no friction losses can occur with the present invention as areexperienced in conventional arrangements. One of the two shafts may bedesigned as a hollow shaft into which the other shafts coaxiallyprotrudes.

The rotor of the electric machine is preferably rotatably connected withthe disk set by means of a spring element which is at least partiallycompliant in the axial direction. With the rotor being in a position inwhich the multiple-disk clutch is not in friction engagement, the springelement is not in contact with the rotor and/or the second disk set, orrotates with the same speed as the disk set and the currentless rotor ofthe electric motor, respectively, so that no friction losses occur.

According to the invention the electric machine is an asynchronousmachine or a permanent field machine, with permanent field machinescontrary to asynchronous machines though being of especially smallinstallation size generate long-term losses in the stator even in thenon-driven condition. Principally, other types of machines, e.g.so-called switched reluctance machines, are possible. That which isdecisive is that the machine can be manufactured economically, has along life, can provide a sufficiently high holding torque, and covers aspeed range of up to approx. 8000 rpm (i.e. the maximum speed of theshaft carrying the rotor of the electric machine).

In a preferred embodiment of the invention an element (e.g. the spindle)of the spindle/nut arrangement has an engaged end position and adisengaged end position with one locking location each, and anotherelement (e.g. the nut) of the spindle/nut arrangement has lockingelements which are adapted to lock in the respective locking locationswhen the rotor of the electric machine has reached the respective endposition.

The electric machine is further connected with an electronic controlunit which is adapted to operate the electric machine either as anelectric motor or as an electric generator. For this purpose, theelectronic control unit has a power control capability which depends onthe type (permanent field machine, asynchronous machine or the like) ofthe electric machine and which enables to feed electric power into theelectric machine (electric motor operation) as well as to withdrawelectric power from the electric machine (generator operation). Such anarrangement may be used (also in a combination of several actors) as agenerator or a starter, respectively.

To this end, the electronic control unit is connected with a sensorarrangement which is adapted to provide a signal indicative for therotation of the first shaft. In the case of a sensorless machine controlunit it is, however, also possible to do without sensor. The electroniccontrol unit is further adapted to operate the electric machine in theelectric motor mode with a speed differing from the speed of the firstshaft, for bringing the multiple-disk clutch into the engaged ordisengaged, respectively, position. Depending on the sense of rotationof the first shaft and its speed as well as depending on whether themultiple-disk clutch is to be engaged or disengaged, the rotor of theelectric machine—controlled by the electronic control unit—rotateseither at a higher or at a lower speed than the first shaft. If therotor is not to carry out a relative movement in the axial directionwith respect to the first shaft, the rotor—controlled by the electroniccontrol unit rotates in the currentless condition or by driving in oneof the end positions—in the same direction and with the same speed asthe shaft carrying it.

BRIEF DESCRIPTION OF THE DRAWING

The drawings illustrate details of the invention in various embodiments.

FIG. 1 is a schematic side view of an automatic powershift gearboxaccording to the state of the art.

FIG. 2 shows a section II surrounded by broken lines in FIG. 1, in whichaccording to the invention the hydraulic cylinder/piston arrangement isto be replaced by the arrangement according to FIG. 3.

FIG. 3 shows a schematic cutout of an automatic powershift gearboxaccording to the invention.

DETAILED DESCRIPTION OF THE DRAWING

The gearbox illustrated in FIG. 1 according to the state of the art forpassenger cars with rear-wheel drive has a hydraulic torque converter 3with a converter lockup clutch 2. At higher speeds the converteroperates as a hydraulic torque coupling. The downstream planet gear setsprovide for the gearing up of the other four forward gears and thereverse gear by the optional holding or blocking of their shafts, withthe highest gear comprising gearing up to higher speeds. Themultiple-disk clutches used for blocking are controlled via a hydrauliccontrol system which automatically initiates the gear shift operation asa function of the selected drive positions, the driving speed, thedriving condition, as well as the motor load.

In the first gear which in terms of gearing up corresponds approximatelyto the second gear of a manually-operated gear-box, the clutches 4 and11 are closed. The front planet gear carrier of the gear set 9 bearsagainst the free-wheeling device 15 in the case of tension, while it isoverridden in the case of thrust. The planet gear set 9′ co-rotates as ablock. With the drive position selector lever being in position “1” andthus changing into higher gears being undesired in order to be able todecelerate by means of the engine, the clutch 8 is additionally closed.In the third gear the clutches 4, 5, 7, and 11 are closed, thefree-wheeling devices 15′ and 15″ are overridden. The planet gear sets 9and 10 co-rotate as a block with the transmission ratio of 1:1.

In the fourth gear the multiple-disk clutches 4, 5, 7, and 11″ areclosed, the free-wheeling devices 15, 15′ and 15″ are overridden, andthe planet gear set 9 co-rotates as a block, while the hollow shaft withthe sun gear of the planet gear set 9′ is stationary so that gearing upto higher speeds is effected. Moreover, the hydrodynamic torqueconverter 3 from a certain driving velocity upward.

In the reverse gear the clutches 5, 8, and 11 are closed, the planetgear set 10 co-rotates as a block, and the sense of rotation of theoutput shaft is reversed via the held front planet gear carrier of thegear set 9. At the output side a centrifugal switch 13 is provided whichgenerates pulses for the control system corresponding to the velocity.

The cutout II from FIG. 1 shown in FIG. 2 depicts the multiple-diskclutch 4 with an associated cylinder/piston arrangement 4 a, 4 b. Due tothe fact that the piston 4 b rotates relative to the cylinder 4 a, theinner and outer seals 4 c, 4 d are subjected to considerable stressesand thus to wear. Upon subjection with hydraulic fluid, the piston 4 burges the disk sets of the multiple-disk clutch 4 together.

The cutout of an inventive arrangement shown in FIG. 3 corresponds tothe arrangement of FIG. 2 with respect to its function. Here, however,the cylinder/piston arrangement from FIGS. 1, 2 is replaced according tothe invention by an electric machine which is coupled by a transmissionwith the multiple-disk clutch in order to bring the two disk sets intoor out of friction engagement.

On a first shaft 10 which acts as the drive shaft of the automaticpowershift gearbox a spindle 12 provided preferably with a multiple malethread is arranged so as to be locked against rotation and axialdisplacement. A nut 14 provided with a corresponding female thread isarranged in screwed engagement on the spindle 12. On the outside of thenut 14 a rotor 16 of an electric machine 20 is arranged in anon-rotatable manner. This rotor 16 is surrounded by a stator 18 fromwhich it is separated by an air gap. This allows the rotor 16 to movealso in the axial direction upon a relative rotation about the shaft 10.For both the rotor 16 and the stator 18 the electric details (phase feedlines, stator windings, squirrel cage winding, etc.) have been omittedfor the sake of clarity. The electric machine 20 for an automaticpowershift gearbox of a passenger car may have, for example, a diameterof approx. 150 mm and a thickness of approx. 20 mm.

On the first shaft 10 a first disk set 24 of the multiple-disk clutch 22is arranged slidably in the longitudinal direction but secured againstrotation, which in the example is formed by five circular disk-shapedlamellar disks. A second disk set 26 of the multiple-disk clutch 22 isformed in the example by four circular disk-shaped disks andaccommodated at the inner wall of a second shaft 28 which is formed as ahollow shaft secured against rotation but slidably in the longitudinaldirection. The first shaft 10 protrudes into the interior of the secondshaft 28 formed as a hollow shaft, and the two disk sets 24, 26 of themultiple-disk clutch 22 are in mutual engagement in the radialdirection. The disk of the first disk set 24, which is the remotest fromthe electric machine 20, bears against a support plate 24 a arranged atthe shaft 10 so that the disks of the multiple-disk clutch 22 can becompressed by the electric machine 20.

A spring washer 28 which is at least partially compliant in the axialdirection with its inner edge 38 bears against the face 32 of the nut 14facing towards the multiple-disk clutch 22 in the axial direction. Thespring washer 28 with its outer edge 36 can urge the first disk set 24of the multiple-disk clutch 22 against the second disk set 26 of themultiple-disk clutch 22, if the rotor 16 of the electric machine 20moves along the first shaft 10 towards the multiple-disk clutch 22 oraway from same. Upon an axial movement of the rotor—caused by a relativerotation of the shaft 10—the two disk sets 24, 26 are thus brought intoor out of friction engagement, and the first shaft 10 is securelycoupled with the second shaft 28. Due to the fact that the disks areattached at the respective shaft via a female or male, respectively,toothing so that they are secured against rotation but axially slidable,the second shaft 28 which is accommodated in the housing 30 by means ofthe bearing 32 therefore does not carry out an axial movement relativeto the first shaft 10 which is also accommodated in the housing 30 viathe bearing 34. The direction of the axial movement of the rotor 16depends on the speed and on the sense of rotation of the rotor 16 of theelectric machine 20 relative to the first shaft 10 which is alsorotating during operation.

In order to hold the multiple-disk clutch 22 securely in the engaged ordisengaged position, the spindle 12 of the spindle/nut arrangement isprovided with a detent site each in the form of a recess 42, 44 for anengaged end position and a disengaged end position. The nut 14 of thespindle/nut arrangement comprises corresponding blind holes foraccommodating detent elements in the form of balls 52, 54 which arebiased by means of associated spring elements 46, 48, and which areadapted to engage the respective recess 42, 44 if the rotor 16 togetherwith the nut 14 moves into the respective end position. The thread couldalso be designed in the form of a bayonet catch to provide the two endpositions. The electric machine 20 is connected with an electroniccontrol unit ECU for operating the electric machine 20 either as anelectric motor or as an electric generator.

The inventive configuration permits a generator operation of theelectric machine 20 even with a non-engaged position of themultiple-disk clutch (i.e. with the rotor 16 not locked at the nut 14).

In addition, the electronic control unit ECU is connected with a sensorarrangement in the form of a rotary transducer 60 which supplies asignal to the electronic control unit ECU indicative for the rotation(amount and direction) of the first shaft 10. The electronic controlunit ECU is adapted to operate the electric machine 20 in the electricmotor mode with a speed differing from the speed of the first shaft 10,for bringing the multiple-disk clutch into the engaged or disengaged,respectively, position.

In the disengaged end position, the electric machine can also beoperated as a generator for charging an accumulator 62 connected withthe electronic control unit ECU. This permits to dispense with thegenerator in the automotive vehicle.

If the inventive arrangement is provided at several places in theautomatic powershift gearbox so that the electric machines in theirentirety provide a sufficient power, there is the possibility to bringthe combustion engine electrically driven into rotation with theappropriate position of the individual multiple-disk clutches and theplanet gearboxes. Thus this inventive arrangement also allows todispense with the starter.

Finally it should be noted that the drawings only serve to principallyillustrate the invention; the actual dimensions and proportions offunctional embodiments of the invention may vary therefrom. For thiswith skill in the art it is also obvious and within the scope of theinvention to apply the inventive solution not only with themultiple-disk clutches described but also with dry clutches.

1. An automatic powershift gearbox comprising: at least one gearassembly for selecting a desired gear ratio; at least one multiple-diskclutch capable of being actuated in a controlled manner for holding orreleasing individual elements of the at least one gear assembly, whichallows gear shift operations without interrupting the torque flow, withthe multiple-disk clutch comprising a first and a second disk set whichare in mutual engagement and can be brought into friction engagement byaxial compression against one another, with the first disk set beingconnected with a first shaft, and the second disk set being connectedwith a second shaft and the multiple-disk clutch being coupled by atransmission with an electric machine comprising a rotor and a stator,for bringing the two disk sets into and out of friction engagement bymeans of the electric machine, wherein the rotor of the electric machineis supported rotatably and axially movable on one of the shafts by meansof a transmission device for converting a rotary motion into a thrustmotion, the transmission device comprising: a spindle/nut arrangement,one part of which is substantially rigidly connected with one of theshafts, and the other part of which is substantially rigidly connectedwith the rotor; and said one part of the spindle/nut arrangement has anengaged end position and a disengaged end position with one lockinglocation each, and the other part of the spindle/nut arrangement haslocking elements which are adapted to lock in the locking locations. 2.The automatic powershift gearbox according to claim 1, characterized inthat: the rotor of the electric machine upon current supply carries outan axial movement relative to the second or the first shaft, dependingon its speed and/or sense of rotation, and in a currentless conditionhas essentially the speed of the shaft on which it is carried.
 3. Theautomatic powershift gearbox according to claim 1, characterized inthat: the rotor of the electric machine is rotatably connected with thedisk set arranged at the shaft carrying the rotor, so that upon an axialmovement of the rotor the two disk sets are brought into or out offriction engagement.
 4. The automatic powershift gearbox according toclaim 3 characterized, in that: the rotor of the electric machine isrotatably connected with the disk set by means of a spring element whichis at least partially compliant in the axial direction.
 5. The automaticpowershift gearbox according to claim 2, characterized in that: theelectric machine is an asynchronous machine or a permanent fieldmachine.
 6. The automatic powershift gearbox according to claim 2,characterized in that: the electric machine is connected with anelectronic control unit, with the electronic control unit being adaptedto operate the electric machine either as an electric motor or as anelectric generator.
 7. The automatic powershift gearbox according toclaim 1, characterized in that: the electronic control unit is connectedwith a sensor arrangement which is adapted to provide a signalindicative for the rotation of the first shaft; and the electroniccontrol unit is adapted to operate the electric machine in the electricmotor mode with a speed differing from the speed of the first shaft, forbringing the multiple-disk clutch into the engaged or disengagedposition.